12-Year Follow-Up Study of the C-Reactive Protein in Iranian Middle-Aged Women: Isfahan Cohort Study

Background: As an important inflammatory marker, study of C-reactive protein (CRP) changes over time may lead to better identification of risk factors of cardiovascular disease. We evaluated the relationship between CRP changes and lifestyle, metabolic syndrome (MS) and body mass index (BMI) in middle-aged women and explored potential bias from attrition. Materials and Methods: We studied 1234 participants in the Isfahan cohort study - a longitudinal population-based study of adults older than 35 years living in urban and rural areas of three counties in central Iran. Data were collected every 6 years since 2001 (3 points). Random effects model was used to evaluate the effects of behavioural risk factors and MS on CRP, with pattern mixture model to account for cohort attrition. Results: Mean CRP levels decreased over time (Est = 0.066, P < 0.001). MS (Est = 0.195, P < 0.001), BMI (Est = 0.022, P < 0.001), physical activity (Est = 0.009, P = 0.002) and history of smoking (Est = 0.399, P = 0.002) were independently associated with increases in CRP. Pattern mixture model showed that CRP decreased in participants with monotone measurement (Est = 0.032, P < 0.001), as well as intermittent measurement (Est = 0.022, P < 0.001), with no association in participants who responded at all points (Est = 0.015, P = 0.083). Conclusion: In this study, the rate of changes in CRP level in middle-aged women over time was higher in participants who were irregularly measured than those who measured continuously. MS, BMI and physical activity may be related to the CRP changes over time in middle-aged women.